The private consortium that leased Port Kembla last year has revealed plans to super-size the outer harbour expansion, creating hundreds of jobs and adding millions of dollars to the Illawarra economy.

The proposal to modify the already massive expansion will almost quadruple capacity of the first completed wharf by allowing much bigger ships - and more of them - into the harbour.

NSW Ports Consortium, which leased the port for 99 years from the NSW government for $760 million, hopes to handle 16 million tonnes of bulk cargo a year, up from a previously approved 4.25 million tonnes at its multi-purpose cargo wharf.

Port Kembla port is to accomodate bigger ships.

The first stage of the outer harbour expansion was approved in 2011 and is already under construction, with two more phases due to be rolled out between 2015 and 2037.

The new proposal seeks mainly to adjust plans for the first stage, which is forecast to be finished in 2020.

If approved, it would mean a fourfold increase to the bulk cargo capacity of the first terminal, as well as deeper dredging to allow larger ships - called Cape and Super-Post Panamax vessels - to use the terminal and container wharves.

Ship arrivals would also increase by about 170 vessels a year.

According to NSW Ports chief executive at Port Kembla, Dom Figliomeni, each arrival adds about $1 million and four port-related jobs to the Illawarra economy.

The new owners of Port Kembla hope to amend an expansion plan to allow for more and larger ships.

This means 680 extra jobs and $170 million would be generated from ship arrivals alone.

Mr Figliomeni said the investment in the outer harbour project, previously stated to be about $700 million, would not increase dramatically as the modifications were mainly designed to make better use of the existing plans.

"It doesn't in any way change the operations, it just increases the capacity," he said.

He said the new owners were responding to extra demand for bulk container trade as well as "significant market interest" from potential customers in the minerals export industry.

"Bulk products are normally in the millions of tonnes, and based on the inquiries we have had, which include everything from bauxite through to iron ore, the 4.25 million tonnes was not going to be enough to handle those two commodities," he said.

"So we looked at putting state-of-the-art equipment on [the wharf] and managing all the environmental aspects to come up with a realistic capability of that first wharf - and that's 16 million tonnes."

The proposal says most of the extra cargo would be transported by rail, with up to 13 trains a day - nine more than previously approved - accessing the outer harbour.

To handle increased capacity, NSW Ports has highlighted necessary upgrades to the Unanderra to Moss Vale rail line, which it says is "under-utilised", or construction of the Maldon-Dombarton link.

"Our preference for the projects is that the Maldon-Dombarton line is provided sooner rather than later, but we understand there has to be a viable business case for that," Mr Figliomeni said.

"And as we bring new business into the port, that adds a little bit more weight to the business case for these rail lines."